I believe the previous thread also included the good 'zzuf' ? telling us there were some older unmodified VAMPs that were only flown dual with an instructor (never solo students) because the VIBES were not for the faint of heart. Meanwhile:
RAAF Goblin Modification 1087
“7. In an endeavour to eliminate the critical vibration ranges of 7,800-8,650 rpm & 8,800-9,200 rpm in Goblin engines, a modified impellor and diffuser assembly was introduced. This modification 1087 has been incorporated in approximately 90 out of 150 engines.
8. Since the incorporation of this modification, a considerable number of minor defects and three major accidents overseas have led to extensive investigation and the following restrictions, which were necessary because of the impellor vane flutter which resulted in cracking and break-up of the impellor back plate, were imposed:-
(a) Operation in the following rpm ranges is prohibited except when passing through the range when changing power:-
(i) 10,350 to 10,650. (ii) More than 10,350 above 25,000 feet.
9. It is emphasized that failure to adhere to these limitations could cause impellor failure in a very short time.
10. The rpm ranges 7,800-8,650 & 8,800-9,200 should be avoided whenever possible. They must never be used for cruising or prolonged descent.”
